Craters on Mercury are oases for water ice, organic molecules

Polar region holds material left over from the early days of the solar system.

Two craters in the Goethe basin near the planet Mercury's north pole. Portions of these craters are permanently shadowed, meaning they are never subjected to sunlight. Similar craters have recently been found to contain water ice and organic materials.

According to our best models for the formation of the Solar System, comets and meteorites bombarded the planets in their early days. This bombardment brought water to Earth, Mars, and the other terrestrial worlds. But Mercury is an airless body and is much closer to the Sun, so its daytime surface temperature reaches 426°C. That's hot enough to make sure that any exposed surface water would have evaporated long ago, along with other volatile substances.

However, a new set of measurements from the MESSENGER probe has revealed the probable presence of water ice in shadowed craters near Mercury's poles. Using laser and radar reflection along with measurements of neutron emissions, MESSENGER scientists found patches of reflective material that alternate with much darker regions than the average planet surface. This data suggests the presence of both ice and complex organic molecules, both of them probably left over from when the Solar System was young.

The presence of water on Mercury had been suspected since as early as 1992, due to Earth-based radar reflection experiments. These measurements were ambiguous enough that more direct observation was desirable. Enter MESSENGER: the MErcury Surface Space ENvironment, GEochemistry, and Ranging probe, which has been orbiting Mercury since 2011. MESSENGER carries a variety of instruments for measuring surface features and magnetic fields, along with more ordinary cameras for imaging.

Among those devices are radar and laser range-finders, which (in addition to registering distance) measure the reflective properties of the surface. It's also got a neutron detector. Neutrons are emitted by radioactive materials on Mercury, including those that are made radioactive by cosmic rays. Measuring the neutron spectrum (numbers and energy) helps determine the chemical composition of surface materials, particularly the hydrogen content.

The results from both the reflection and neutron analyses were consistent: several craters in Mercury's polar regions provide sufficient shadow for stable water ice. The large craters named Prokofiev and Kandinsky were both found to contain significant radar-bright (RB) patches, indicating highly reflective materials. (Craters on Mercury are commonly named for famous artists, authors, composers, and the like. As a fan of both Prokofiev and Kandinsky, I approve.)

The size of the reflective patches matched the total proportion of each crater that lies in permanent shadow. Unlike Earth, Mercury has almost no axial tilt, so it doesn't experience seasons. This leaves many deep craters in the polar regions untouched by sunlight and means that if they're shadowed now, they will generally remain that way.

The radar reflection study found that some of Mercury's ice is in the form of frozen ponds. Other ice—still detectable through scattered light and neutron emission—is covered in dark, highly nonreflective material up to 20cm deep. The researchers determined this dark layer contains far less hydrogen than should be present if it were a water-saturated material. Complex organic—meaning carbon-containing—molecules are both dark in color and relatively common components of asteroids, meteorites, and comets.

The clear discovery of water ice on Mercury meshes nicely with similar finds on the planetoid/asteroid Vesta and the Moon. The abundance of both water and organic materials is consistent with models of the early Solar System, in which bombardment by comets and meteorites deposited both types of molecules onto the terrestrial planets and moons.

Other ice—still detectable through scattered light and neutron emission—is covered in dark, highly nonreflective material up to 20cm deep

That is a lot of organic matter. I'm guessing a bitumen - like mixture of primordial goo? Perhaps enough to insulate the surface of the ice and allow some entertaining complex reactions to occur? Life finds a way??

All it would need is some time and some energy source... Since it's supposed to have a molten core, perhaps some geothermal (what would the appropriate term here be?) heat?

Would be a worthier goal than a moon mission. And astronauts climbing down into billion-year old darkness full of water ice and organic goo would be fun to watch. Lots of free energy raining down on you if you land on the rim too. Better bring a shade though ;-)

"The abundance of both water and organic materials is consistent with models of the early Solar System, in which bombardment by comets and meteorites deposited both types of molecules onto the terrestrial planets and moons."

Note though that Earth & moon D/H hydrogen isotope ratios are not consistent with dominant contributions from either comets (at many oom higher ratios) or main belt asteroids (at perhaps twice the ratio).

Bitumen is hydrocarbons that are on their way to coal by way of kerogens. Kerogens form from a generic geological process that first strips predominantly oxygen and then hydrogen from the carbons under heat and pressure.

I've always been puzzled by this. Maybe I misunderstand. It seems explanations often lead to the conclusion that water and - heck, even organic material - might have been brought to our solar system by incoming asteroids. This begs the question, to me, of how water - and, heck, organic material - formed on those incoming asteroids. Right? Why couldn't the material(s) have formed "here" instead of "there"? Or is it, that I misunderstand, and that the asteroid hits *caused* the formation of this (these) material(s)?

However, a new set of measurements from the MESSENGER probe has revealed the probable presence of water ice in shadowed craters near Mercury's poles. Using laser and radar reflection along with measurements of neutron emissions, MESSENGER scientists found patches of reflective material that alternate with much darker regions than the average planet surface. This data suggests the presence of both ice and complex organic molecules, both of them probably left over from when the Solar System was young.

A few months ago - scients swear they had evidence of water on BOTH the Moon and Mars - which turned out to be false so far.

But Mercury has ice ?? Bullshit.

Even if there are spots on Mercury where it does not get blasted by the heat from the Sun - the residual / in-direct / fall-off heat in those areas would still be significantly high (most likely too high for water - much less ice to be collected there).

Think of it like this - in the peak of the summer time - hot day that reaches 90˚-100˚ - the shade from a large tree or building is still high enough to not sustain ice. It's "cooler" relative to being in direct sun - but it's still hot relative to winter periods.

A few months ago - scients swear they had evidence of water on BOTH the Moon and Mars - which turned out to be false so far.

What?

Quote:

Even if there are spots on Mercury where it does not get blasted by the heat from the Sun - the residual / in-direct / fall-off heat in those areas would still be significantly high (most likely too high for water - much less ice to be collected there).

What residual heat? There's virtually no atmosphere. Temperatures at the surface range from 100 Kelvin (-173 Celsius) to 700 K depending on whether they're in light or shadow. The craters are in permanent shadow and there's no air to carry heat into them.

Quote:

Think of it like this - in the peak of the summer time - hot day that reaches 90˚-100˚ - the shade from a large tree or building is still high enough to not sustain ice. It's "cooler" relative to being in direct sun - but it's still hot relative to winter periods.

Because we have this little thing called "air" which helps redistribute thermal energy.

However, a new set of measurements from the MESSENGER probe has revealed the probable presence of water ice in shadowed craters near Mercury's poles. Using laser and radar reflection along with measurements of neutron emissions, MESSENGER scientists found patches of reflective material that alternate with much darker regions than the average planet surface. This data suggests the presence of both ice and complex organic molecules, both of them probably left over from when the Solar System was young.

A few months ago - scients swear they had evidence of water on BOTH the Moon and Mars - which turned out to be false so far.

But Mercury has ice ?? Bullshit.

Even if there are spots on Mercury where it does not get blasted by the heat from the Sun - the residual / in-direct / fall-off heat in those areas would still be significantly high (most likely too high for water - much less ice to be collected there).

Think of it like this - in the peak of the summer time - hot day that reaches 90˚-100˚ - the shade from a large tree or building is still high enough to not sustain ice. It's "cooler" relative to being in direct sun - but it's still hot relative to winter periods.

Mercury doesn't have an atmosphere to hold in radiant heat. Anything not in contact with the direct exposure to sunlight is exposed to the cold vacuum of space. Hence... any shadowed areas at the poles, where sunlight never reaches, can indeed hold ice.

If I'm understanding this correctly, we're starting to find organic matter (in the "organic chemistry" sense) in all kinds of surprising places, as long as the ambient conditions support the formation of such matter. Seems to me that it's testament to the uncanny strength of the carbon/carbon bond, so it kind of makes sense when you think about it.

Makes me wonder; could there be subsurface ices on Mercury, even on the sunward side? Specifically I am thinking about the viability of establishing a colony on Mercury (in one of these craters) and then mining not only the crater ices, but perhaps massive underground mines that circumnavigate the planet at depths of 1km+.

Mercury would seem to be an ideal body for colonisation. Massive amounts of free power, low gravity...seems like a great place to mine and refine raw metals. I do wonder however if there are enough volatiles available to sustain more than a handful of people for a very short time.

I've always been puzzled by this. Maybe I misunderstand. It seems explanations often lead to the conclusion that water and - heck, even organic material - might have been brought to our solar system by incoming asteroids. This begs the question, to me, of how water - and, heck, organic material - formed on those incoming asteroids.

Great questions!

The basic theory on water is based on observations of how volatiles are plenty, and besides giants or freshly supplied moons (Titan), are frozen in the outer system. Especially for water the radiation from the young Sun would have set up an "ice line" (aka "snow line") in the protoplanetary disk.

This would predict the mass content of water in asteroids, where the majority has ~ 10 % water by mass, and comets much more. It would also predict the dryness of terrestrials, who have ~ 0.05 % water by mass. (But see the tension with later models as described below, where the problem is to get rid of the water in the first place!)

Luckily, or we would have no continents.

Recently it has been suggested that the same would happen with carbon, a "soot line". Carbonaceous chondrites have a lot of carbon, and it is predicted that superEarths accreting outside the soot line could have ~ 30 % carbon crust by mass.

Luckily we don't have that as it would set up an outer diamond crust and bar cells from necessary metals to make vital ribozymes or enzymes. Instead we have siliceous minerals.

But, to finish this story, it is unlikely that asteroids and comets have supplied inner terrestrials with a dominant part of water. The hydrogen isotope D/H ratio of asteroids is ~ 2 times larger than Earth since they formed in a colder part of the disk. And comets are worse by many orders of magnitude.

Instead the roughly same water content found in Earth, Moon and Mars initial mantle by various samples (zircons, Apollo samples, martian meteorites) can be predicted by a disk mechanism, as opposed to the differential rates suggested by impactor delivery. Recently such an innate mechanism was found. [ http://astrobites.com/2012/07/25/snow-l ... -water-go/ ]

"Consistent with previous work, the turbulent model has the ice line crossing an AU just about a million years after disk formation – barely any time to form planets! By contrast, the model that includes a turbulence-free dead zone has an inner icy region and a central ice-free region. The latter is attributed to a small amount of turbulence due to self-gravity that heats the outer region of the dead zone.

This is very exciting – after t~1 million years, there is a growing ice-free region right around the Earth’s orbit! This resolves the discrepancy of previous models, and provides ample time for an ice-free Earth to evolve. Further work will be necessary to validate this model. If it proves consistent, then we may have reconciled planet formation theory with the water-poor Earth: Regions of low turbulence in the protoplanetary disk allow formation of water-poor terrestrial planets."

On the other hand it is known _some_ late bombardment by asteroids was present, or we would have little to no rare earth metals in the crust.

Note by the way from the figure in the link that Mercury, now at 0.3 - 0.4 au, could have been within the dynamic inner icy region most of its formation time. Water as from such a source in terrestrials comes from hydrogen and oxygen trapped in the mantle material, which are later released by volcanism and reconstituted as water sooner or later. Mercury should have a higher innate water content (by mass) than Earth has, and it may well be that some of the ice we now see has its source within rather than without.

A few months ago - scients swear they had evidence of water on BOTH the Moon and Mars - which turned out to be false so far.

Both water within and without Moon and Mars have been unambiguously observed.

The inner water content of Moon is observed in crystal water inclusions of volcanic Apollo samples. The outer water content came from similar observations as described here, but also from observations when the LCROSS impactor hit a polar region.

The inner water content of Mars is observed in crystal water inclusions of volcanic martian meteorite samples. The outer water content came from similar observations as described here as well as from observations when the 3 latest rovers found geological formations that only water can make, but also from analyses of water ice and observations of saline ("anti-freeze") water drops by Phoenix.

And as I noted in another comment, we now have a compelling theory for why that is. The alternative is that there is something fundamentally wrong with planetary science understanding of protoplanetary disk behavior.

All this, except the planetary science results, is already in the Wikipedia with references, I'm sure.

What is your reference for any problems with any or all of these observations?

...as from observations when the 3 latest rovers found geological formations that only water can make...

There's no such thing.

I understand you want to believe that there's water on those dead rocks, and you want to believe that presence of minuscule amounts of ice has some non-trivial significance. However the desire to believe in a certain reality has nothing to do with science, more with religion.

We can argue all we want about the facts, and the dearth of information that we have will only fuel the argument, instead of quenching it which would be the logical thing. However the more important question is not what the facts are, but whether those facts turning out one way or the other really would change anything about our understanding of the universe. My bet is that they won't.

We can argue all we want about the facts, and the dearth of information that we have will only fuel the argument, instead of quenching it which would be the logical thing. However the more important question is not what the facts are, but whether those facts turning out one way or the other really would change anything about our understanding of the universe. My bet is that they won't.

They already have. You just don't realize it because you're living in a world that's already seen other planets and moons close-up.

...as from observations when the 3 latest rovers found geological formations that only water can make...

There's no such thing.

That is not what the geologists say. From memory, so possibly mistaken:

1. Spirit: A hydrothermal vent, with its quartz grains. Can't possibly be formed by anything but a system with water somewhere.

2. Opportunity: Cracks with gypsum. Can't possibly be formed by anything but water.

3. Curiosity: Stream deposit conglomerate, with stones rounded by water conditions, but not liqCO2 conditions, transport. Can't possibly be formed by anything but water.

As for the rest of your comment, these observations tests the natural hypothesis of water, natural all by itself and natural by knowing the properties of the system bodies and natural by knowing the formation of the protoplanetary disk (see my earlier comment). This happens to be extremely well motivated, but it is really no different from testing other science theory.

So you've moved on from being factually incorrect (and having your errors pointed out rather clearly) to...what? Getting pissy about a space probe?

You should write a letter to the editor of your local newspaper!

Factually incorrect? When and about what? About fairy tales that cannot be experimentally falsified?

Your snark is entirely misdirected.

The part about where the clear scientific evidence points clearly to water being on the Moon and Mars. And the other part where you compared the airless vacuum of Mercury with sitting under the shade of a tree on a hot summer's day.

Unless you're a geologist with some kind of published proof that hydrothermal vents with quartz grains can be formed outside of liquid water?

So you've moved on from being factually incorrect (and having your errors pointed out rather clearly) to...what? Getting pissy about a space probe?

You should write a letter to the editor of your local newspaper!

Factually incorrect? When and about what? About fairy tales that cannot be experimentally falsified?

Your snark is entirely misdirected.

The part about where the clear scientific evidence points clearly to water being on the Moon and Mars. And the other part where you compared the airless vacuum of Mercury with sitting under the shade of a tree on a hot summer's day.

Unless you're a geologist with some kind of published proof that hydrothermal vents with quartz grains can be formed outside of liquid water?

No?

Then your opinion on the matter is worth exactly jack.

Please.

First off, you confuse me with someone else in regard to comparing "the airless vacuum of Mercury with sitting under the shade of a tree on a hot summer's day." If you insist on picking on me, at least bother to figure out who said what.

Second, while water is clearly present, there has been no evidence that its has ever flown and participated in forming the observed phenomena. There's just a hypothesis, which I am willing to accept as the most feasible truth merely based on Occam's razor, but I do not appreciate it being mistaken for a straightforward fact.

Third, calling on authority ("Unless you're a geologist ") discredits you completely in my eyes. I choose to participate anonymously in those discussion exactly because I do not wish degrees and titles to get in the way of logic. I'm sure that many on Ars have those, but I appreciate when they convince me on the merit of their arguments, not on that of their past glory.

Third, calling on authority ("Unless you're a geologist ") discredits you completely in my eyes. I choose to participate anonymously in those discussion exactly because I do not wish degrees and titles to get in the way of logic. I'm sure that many on Ars have those, but I appreciate when they convince me on the merit of their arguments, not on that of their past glory.

Appeals to authority aren't always a logical fallacy. For example if all geologists and paleontologists agree that dinosaurs walked the Earth until around 65 million years ago, and the Earth is several billion years old, then their opinion is going to hold a lot more water than some random poster on the Internet spouting Young Earth Creationist garbage.

So I repeat: unless you have some kind of proof that the evidence of water on Mars and the Moon can be caused be something other than water, then you're going to find it terribly hard to get anyone to listen. You just end up like every other anonymous contrarian on the Internet claiming "Hurr durr scientists are wrong" without anything to back it up.